The principle aim of this proposal is the comparative evaluation of the immunogenetic basis allograft rejection. These incompatibilities will be studied as they relate to mechanisms of cell-mediated and humoral immunity from the phylogenetic and developmental standpoints. The approaches that bear on this central goal are as follows: (1) to further characterize the mechanisms of cellular immunity as they relate to histopathology of allograft rejection. (2) To relate gross and histological manifestations of allograft rejection to the immunogenetic characteristics of a given species. (3) To further characterize the developmental aspects of cellular immunity as defined by embryonic transplants, tolerace and the graft vs. host (GVH) reaction. (4) To combine long-term studies of the phylogeny, ontogeny and kinetics of immune responses, with particular emphasis on the establishment of immunogenetic rules and evolutionary trends. (5) To study the evolutionary development of T cells (thymus derived), B cells (bursal or bone marrow cells) and macrophages.